The French plastics processing group Plastic Omnium S.A. (HQ: Rue du Parc 1, F-92593 Levallois) introduced a new patented process called “Express” (Extrusion-Pressage) for the production of long fibre reinforced thermoplastic parts. The “Express” process consists of laying the material in the tooling using an extruder operated along two horizontal axes, then of closing it using vertical compression. According to the company, this technology allows the production of structural parts with excellent geometry (low internal stress in the part) and excellent uniformity due to the very good distribution of filling rate.

The first industrial application of “Express” is the bumper bar of the Citroën Xantia phase 2, which is produced in Plastic Omnium´s Guichen factory (Ille-et-Vilaine). On the previous model Citroën Xantia, the bumper bar was made of GMT (glass mat reinforced thermoplastic), a solution that was considered as too expensive in the case of Xantia phase two. “Express” technology not only offers lower part prices when compared to GMT but it also provides higher impact resistance (+50%) and lower clamping forces (500 t instead of 1500 t) when compared to LFI (Long Fibre Injection).

The compound used for this application is made of polypropylene reinforced with 30% of glass fibres. The granules are prepared in a two-step process. At first, the fibres must undergo a surface treatement aiming to improve impregnation and quality coupling. Then, the thermoplastic is pultruded with the fibre, leading to granules of 23 mm in length and 2-3 mm in diameter.

In order to achieve even greater mechanical properties, Plastic Omnium has developped a second process called HTPC (Hybrid Thermoplastic Composite), allowing local reinforcement of the part. This patented process consists of putting the hybrid TP reinforcements (continuous glass fibre and plastic wowen together) in the tooling, then, like for the “Express” process, of laying a second material (reinforced glass fibre, both long and not) with an equivalent matrix.

“Local reinforcement make it possible to fulfil the very localized stresses of the part, thus leading to very large weight savings”, says Plastic Omnium. At present, the base resin used is polypropylene, but the firm is already developing the use of polyamide or PET so as to be able to offer modules and resistances to even higher temperatures.

Potential applications for “Express” and HTPC processes in the automotive industry include bumper and dashboard bars, crash boxes, engine undertrays, spare wheel wells, technical front panels, technical front quarter sections, opening element structures and bulkhead modules.